1. Field of the Invention
The present invention relates generally to the field of optical signal processing, and, more particularly, to a method and apparatus for obtaining the doppler transform of a one-dimensional signal by re-writing the signal into a two-dimensional raster form image pattern and thereafter subjecting the two-dimensional image to an optical linear transformation.
2. Description of the Prior Art
Triangulation is a procedure commonly used to locate accurately the position of an object of interest by means of bearings from two fixed points a known distance apart. It is further known that this procedure can be used to locate the position of an underwater object through the use of sonar. Specifically, a sonar signal containing information indicative of an object of interest received by a first hydrophone array positioned at a known location can be correlated with a reference signal received by a second array a known distance from the first array to provide information regarding the position of the object.
When the object of interest is a moving object such as a ship or the like, the obtaining of accurate positional information is complicated by the fact that it further becomes necessary to correct the signal for doppler shift. If the velocity of the moving object is known, this can be accomplished fairly easily. However, when the velocity is not known, it becomes necessary to carry out what is essentially a trial and error procedure to ascertain the precise magnitude of the doppler shift by which the signal must be corrected. Specifically, the sonar signal, which is in the form of a long linear trace, is processed for a large number of different dopper levels, for example, 3,000 or more, and each of these doppler compensated signals is then examined and analyzed to ascertain the proper one.
In carrying out this procedure it is necessary to doppler transform the signal by stretching or contracting it for each of the levels, and then record each transformed signal for evaluation.